1. Field of the Invention
The present invention relates an object detection device mounted on a vehicle and the like and its method, and more particularly to an object detection device for detecting the image area having a high possibility of including an object, such as a pedestrian and the like of an image picked up by a single-lens camera mounted on a vehicle and the like and its method.
2. Description of the Related Art
As to the present vehicle-mounted preparatory prevention system of forward-collision accidents, various methods are proposed.
For example, Patent Document 1 proposes a system for detecting the size and position of a vehicle by detecting light in an image picked up by two infrared cameras.
As a system for targeting and detecting an object, such as a pedestrian and the like, Non-patent Document 1 proposes one method.
The traditional object detection method of a pedestrian and the like disclosed by Non-patent Document 1 uses the fact that the shape of a pedestrian is almost axially symmetric and extracts the candidate area of the pedestrian by evaluating the axial symmetry in an image local area.
The object detection method disclosed by Non-patent Document 1 evaluates the symmetry of a brightness image and an edge image in a rectangle area of each pixel, supposed to enclose a person when assuming that the pixel represents its feet, on the basis of the object size and the perspective projection conditions (its detailed method is not disclosed). In this case, when there is a plurality of rectangle areas whose symmetry evaluation value is equal to or more than a threshold on the symmetry axis, one in which the symmetry of a vertical edge image and an evaluation function (undisclosed) whose component is a vertical edge density are maximums is selected.
However, assuming that there is the same vertical symmetry axis from the top until the bottom of a rectangular area supposed to enclose a person, sometimes a problem occurs.
For example, in the case of a person that walks sideways in a large foot step, sometimes the symmetry of a lower-body cannot be obtained in the same symmetry axis as the upper-body. In this case, a small area is selected in the further upper section than essential.
This causes a problem that when converting a distance from its own vehicle, it is detected farther away than actual since the rectangular area decreases. In a small rectangular area, there is a possibility that a rectangular area for only the upper-body is discarded by the detailed determination of pattern recognition in the later stage, which deteriorates the detection function.
FIG. 1 shows the above-described problem.
FIG. 1 typically expresses an image in which a person is walking.
When a person is walking, it is difficult to obtain a symmetry axis passing through from the upper-body until the lower-body. In FIG. 1, a symmetry axis 2 against which the lower-body is horizontally symmetric deviates from the symmetry axis 1 of the upper-body. In the system of Non-patent Document 1, although the image of this one person must be essentially detected like a rectangular area 4, only the rectangular area 3 of the upper-body is detected and the lower-body is processed as another rectangular area.
However, in Non-patent Document 2, two cameras are mounted on a vehicle and the distance of a rectangular area is obtained by measuring the distance by a stereo image processing method. Then, the correction of a rectangular area is applied to a position and a size led by the perspective projection conditions, on the basis of the obtained distance. However, in this method of Non-patent Document 2, since a mechanism for a stereo image process is necessary, for example, since two cameras are necessary, costs become high.
When its contrast with the background is insufficient and the image 5 of the lower-body is not clear, a smaller area 6 is selected in the further upper section than essential since the vertical edge is not sufficiently extracted as shown in FIG. 2A.
When there is a symmetry texture 7 (painting, manhole, etc.) at its feet, a large rectangular area 8 is selected in the further lower section than essential as the rectangular area for the pedestrian, as shown in FIG. 2B since the vertical edge is taken into consideration.
In view of the above, it is an object of the present invention to provide an object detection system and method having a mechanism for determining the area of a target object with higher accuracy using only an image picked up by a single-lens camera without performing a stereo image process.
It is another object of the present invention to provide an object detection system and method with a higher object detection function at low costs.    Patent Document 1: Japanese Patent Application No. 2003-230134    Non-patent Document 1: Massimo Bertozzi, Alberto Broggi et al., “Vision-based Pedestrian Detection: Will Ants Help?”, IEEE Intelligent Vehicles 2002, volume 1, pages 1-7 (June 2002).    Non-patent Document 2: Alberto Broggi, Massimo Bertozzi at el., “Pedestrian Localization and Tracking System with Kalman Filtering”, IEEE Intelligent Vehicles 2004, pages 584-589 (June 2004).